The relationship between water activity and moisture content at a given temperature may be referred to as a moisture sorption isotherm. Moisture sorption isotherms show the relationship between water activity and moisture content for a particular sample at a given temperature. For example, a graph of a moisture sorption isotherm may illustrate a relationship between water activity and moisture content by showing moisture content on a y-axis of the graph and water activity on an x-axis of the graph. A moisture sorption isotherm may be used to estimate shelf-life of a food product. Moisture sorption isotherms may be particularly useful in developing new food products, in characterizing ingredients, in determining packaging requirements for food products, and in various areas of research and development requiring a knowledge of the relationship between water activity and moisture content for a particular product at a given temperature.
A traditional method for obtaining a moisture sorption isotherm may be to place a food sample, either dried (absorption), hydrated (desorption), or native (working), into a controlled humidity chamber at constant temperature. The next step may be measuring the weight of the sample until the weight reaches equilibrium. This process may need to be repeated numerous times to acquire enough data points to generate a useful isotherm. The entire process may take up to three weeks. The large amount of time and labor that may be required to obtain an isotherm may be prohibitive for obtaining isotherms in various instances.